Contamination of semiconductor devices by mobile ions such as Na+, K+, Fe+ etc. introduced during the manufacturing process is an issue in semiconductor device manufacturing. Whenever an electric field is maintained across a silicon oxide layer for long periods of time, contaminating mobile ions migrate towards an interface between the silicon oxide and neighboring material such as silicon. For example, in MOS field effect transistors, the mobile ions tend to accumulate at the junction between the gate oxide and the underlying silicon channel region. The contamination can over time eventually build up to a point where the threshold voltage of the device is noticeably affected which is undesirable.
For these and other reasons, there is a need for the present invention.